Pollutants and emerging concerns

We've known about many of the pollutants that the MPCA monitors in Minnesota waters for decades. Some, such as nitrogren and phosphorus, have been an issue for a long time, and we know a great deal about how they affect the environment. Other pollutants, such as chloride, have been recognized as problems more recently, and still others we may not know about yet. The development of new products and chemicals and our knowledge about what contaminants do in water and what affect they have on the environment and human health are constantly evolving, and the challenges we face may change down the road.

nitrate molecule


Nitrogen is a key, high-volume pollutant in state waters and its concentrations in both surface and groundwater have been increasing over time. The MPCA released a report on nitrogen pollution in 2013, indicating that agricultural fields using artificial subsurface drainage (drain tile) are a key source of nitrogen pollution. Nitrate (a form of nitrogen) in lakes, rivers, and streams is toxic to fish and other aquatic life; in drinking water, it's potentially harmful to humans. Proposed reductions in nitrogen will benefit both Minnesota waters and water downstream from us, particularly the oxygen-depleted “dead zone” in the Gulf of Mexico.

Periodic table entry for phosphorus represented by symbol P, atomic number 15, and atomic mass


Phosphorus is a common element in agricultural fertilizers, manure, and organic wastes in sewage and industrial discharges. Excess phosphorus in lakes, rivers, and streams causes algae to grow. Algae-covered water is less attractive for fishing and swimming — highly valued pastimes in Minnesota and uses that are protected under the federal Clean Water Act. In addition, phosphorus can fuel toxic blue-green algal blooms, which are harmful to people and pets.

Water colored brown by sediment running down soil embankment


Sediment is composed of loose particles of sand, clay, silt, and other substances. It comes from eroding soil and from decomposing plants and animals. Much of the sediment in Minnesota lakes and rivers is contaminated by pollutants, particularly phosphorus. Sediment contributes to turbidity — cloudy water than is harmful to fish and plant life — and, in large quantities, can fill in bodies of water. For instance, the upper seven miles of Lake Pepin could be completely filled in with sediment deposits over the next 100 years, if nothing is done to remedy the problem.

Microscopic view of rod shaped bacteria


Though there are countless numbers of bacteria, viruses, and other microorganisms in the environment, only about 10 percent — known as pathogens — are harmful. If ingested by humans, they can cause illness or even death. Fecal coliform bacteria, and its subgroup E. coli bacteria, can indicate the possible presence of pathogens. Bacterial contamination in lakes and streams typically comes from human, pet, livestock, and wildlife waste. Concentrations in water tends to be lower in the forested and wetland-rich areas of northern Minnesota, and higher in agricultural and more heavily populated areas.

Blue chloride crystals

Chloride, sulfate, and other "salts"

Chlorides, sulfates, salinity, and dissolved minerals are all forms of “salts” that can harm fish and plant life at high concentrations. For example, the salt applied to roads, parking lots, and sidewalks during our icy winters contains chloride, a water pollutant. When snow and ice melts and runs into lakes and waterways, the salt goes with it. It takes only one teaspoon of road salt to permanently pollute five gallons of water. Elevated concentrations of sulfate are a concern for wild rice. Sources include discharges from mining operations, wastewater treatment plants, and other industrial facilities. Options for treating “salty discharges” are limited and expensive, making pollution prevention and source reduction very important tools in reducing the threats posed by these pollutants. Find out more.

Brown waste sludge


Ammonia is a form of nitrogen that is directly toxic to aquatic life. It comes from wastewater treatment plants and animal waste or air pollution and runoff from agricultural land. Water with high concentrations of ammonia allow the chemical to build up in the tissues and blood of fish, and can kill them. Environmental factors, such as pH and temperature, can affect ammonia toxicity to aquatic animals.

Illustration of generic chemical molecule

Pollutants of emerging concern

Recent studies of Minnesota’s waters show that a wide variety of unregulated chemicals, such as pharmaceuticals, fragrances, fire retardants, and insecticides, are ending up in lakes and rivers. Many of these substances have properties that can interfere with the functioning of hormones in animals and people. Some mimic the effects of hormones in animals and negatively impact growth and development. These endocrine-active compounds are not acutely toxic at the levels normally found in the environment, but over time can impact organisms at very low concentrations. Sources of these chemicals to waters include wastewater discharges, runoff from animal agriculture, and air pollution.

More about Contaminants of emerging concern.


Mercury is a neurotoxin that contaminates air, land, and water. The largest sources of the mercury in Minnesota’s environment include coal burning, industrial boilers, petroleum refineries, metal smelters and shredders, taconite, and incinerators. However, about 90% of the mercury deposited on Minnesota comes from other states and countries. Mercury in the air eventually settles into water or onto land where it can be washed into water. Once deposited, bacteria can change it into methylmercury, a highly toxic form that builds up in fish, shellfish, and animals that eat fish. Fish and shellfish are the main sources of methylmercury exposure to humans. Methylmercury poses the greatest threat to children, whose nervous systems are still developing, or to those who rely on fish for much of their diet. The Minnesota Department of Health makes recommendations about how often Minnesotans should eat fish from lakes and rivers around the state. With an MPCA search tool, you can find out if a specific body of water has elevated levels of mercury.

Dinner plate with fish